(1) Field of the Invention
The present invention relates to an ink supplying device adapted for a rotary press used for printing news papers. More particularly, the present invention relates to an ink supplying device especially adapted for specific types such as an off-set type printer, which is provided with an ink circulation system between an ink supplying unit and an ink reservoir, and an ink temperature control system.
(2) Description of the Prior Art
Conventional ink supplying devices provided with an ink circulation system between an ink supplying unit such as an ink fountain and a fountain roller and an ink reservoir such as an ink tank have been disclosed in Japanese Patent Publication No. 35-12862 and U.S. Pat. No. 4,384,523. In detail, the former invention teaches one type of ink circulation system comprising an overflow wall formed on an ink tank (or ink fountain) and a conduit pipe adjacent to it. The conduit pipe is communicated with a main ink tank (or ink tank) so that ink is fed from the main ink tank to the ink tank through a pump and overflowed ink is fed back to the main ink tank through the conduit pipe from the overflow wall. This prior art is a typical example of a basic ink supplying device with an ink circulation system. This circulation system provides an effect that the ink stored in the ink fountain can be kept at the constant level and further the stagnation of the ink in the fountain is not generated by the circulating flow. However this device is not free from some problems caused by this ink circulation. The ink temperature is easily increased by the circulation between the ink tank (ink fountain) and the main ink tank (ink tank) and the heat generated from the driving unit of printing apparatus. The viscosity of ink becomes low and thus the quality f printed surface may become poor.
The later invention teaches an example of ink circulation system with a cooling unit which can cool the ink in a circulating tank (ink tank). This cooling unit may prevent the quality of printed surface from becoming poor to some degree. However, when the viscosity is very high and the fluidity is relatively low, the heat is not quickly transmitted in the ink. Even if the ink is subjected to a large scaled cooling device, the heat is not smoothly transmitted because the fluidity becomes poor as temperature decreases. Also this invention can not provide sufficient effect.
In these conventional systems for circulating ink between the ink fountain and the ink tank, the ink may become tacky owing to thixotropy phenomenon of the ink per se after the circulation is not actuated for a while. Such tacky ink causes ink spreading to worsen because of poor fluidity. Thus enough ink is not applied to the printed surface, thereby causing problems such as poor quality, vague printed surface, lack of clearness, and so on.